Flash unit

ABSTRACT

In a flash circuit of a flash device, a Zener diode ( 37 ) is connected to a tap point ( 23   f ) located at an intermediate position of a secondary coil of an oscillation transformer ( 23 ). The oscillation transformer ( 23 ) and an oscillation transistor ( 22 ) constitutes an oscillation circuit. A potential at the tap point ( 23   f ) changes proportionally to a voltage charged in a main capacitor ( 41 ). When the main capacitor ( 41 ) is charged up to a set voltage, the Zener diode ( 37 ) conducts a Zener current, which activates a stopping transistor ( 38 ) and thus deactivates the oscillation circuit. When a flash charge switch ( 51 ) is turned on, an end of a light guide portion of a charge condition indicator ( 60 ) protrudes out of a lens-fitted film unit. When the main capacitor ( 41 ) is charged up to the set voltage, a light emission element starts lighting and the light from the light emission element is projected from the end of the light guide portion.

This application is a division of application Ser. No. 09/486,338, filedon Feb. 25, 2000, now U.S. Pat. No. 6,345,156B1. Application Ser. No.09/486,338 is the national phase of PCT International Application No.PCT/JP98/03701 filed on Aug. 21, 1998 under 35 U.S.C. 371. The entirecontents of each of the above-identified applications are herebyincorporated by reference.

FIELD OF THE ART

The present invention relates to a flash device, and more particularlyto a flash device which is suitable for being incorporated in alens-fitted photo film unit that contains a roll of photo filmstrip andis provided with a simple photographic mechanism including a takinglens.

BACKGROUND ARTS

When the subject brightness is so low that a proper exposure would notbe provided without any artificial illumination, a flash device is oftenused to project light toward the subject synchronously with the shutterrelease. Since compact cameras and lens-fitted photo film units have aninexpensive lens system of a relative large f-number, most of them areprovided with a built-in flash device. To make a flash photography, itis necessary to charge the main capacitor up to the set voltage prior tothe shutter release. The conventional flash devices start charging inresponse to an actuation of a flash charge switch.

A flash circuit has recently been known, for example from JPA 7-122389,wherein once a flash charge switch is turned on the main capacitorcontinues to be charged even after the flash charge switch is turnedoff. The flash circuit stops charging while the main capacitor is at theset charge voltage. Hereinafter, this type of flash device will bereferred to as an autostop flash circuit.

An example of autostop flash circuit is shown in FIG. 24, which hasfundamentally the same configuration as that disclosed in JPA 7-122389,except some minor differences. In the flash circuit of FIG. 24, when aflash charge switch 200 is turned on, an oscillation transistor 201 isactivated and starts oscillating due to positive feedback of anoscillation transformer 202. The oscillation causes an increase in aprimary current that flows through a primary coil 202 a, i.e. acollector current that flows to the collector of the oscillationtransistor 200. As a result, an electromotive force induces a currentthrough a secondary coil 202 b, and the current charges a main capacitor204 through a rectifying diode 203.

Since the collector current flows through the oscillation transistor201, a latching transistor 205 is turned on. Thereafter when theincrement of the primary current goes down, a back electromotive forceis generated in the secondary coil 202 b, and the current fed back fromthe oscillation transformer 202 to the oscillation transistor 201, i.e.base current of the oscillation transistor 201, begins to decrease.However, a voltage from a battery 206 is applied to the base of theoscillation transistor 201 through the latching transistor 205 as beingin the ON state, the oscillation transistor 201 is not completely turnedoff. Therefore, the primary current starts flowing again, thereby theoscillation transistor 201 continues to oscillate and charge the maincapacitor 204.

A Zener diode 207 with a Zener voltage of 300V is provided for startingconducting a Zener current when the main capacitor 204 is charged up toa set voltage of 300V. Because a base current is applied to a base of astopping transistor 208 due to the Zener current, the stoppingtransistor 208 is turned on. When the stopping transistor 208 is turnedon, the emitter and the base of the oscillation transistor 201 areconnected to each other, so that the oscillation transistor 201 iscompletely turned off, and thus the latching transistor 205 is turnedoff. In this way, the oscillation stops to stop charging the maincapacitor 204 when the main capacitor 204 is charged up to the setvoltage.

In the above autostop flash circuit, since the charge voltage of themain capacitor is applied to the Zener diode to conduct the Zenercurrent for activating the stopping transistor when the charge voltagereaches the set value, the Zener diode must have a high Zener voltage,e.g. 300V, in correspondence with the set charge voltage. As the Zenerdiode with high Zener voltage is expensive, it raises the cost of theflash circuit. In addition, the conventional autostop flash circuitrequires a lot of space for mounting various elements as above which arenecessary for the automatic continuation and stopping of charging.

Meanwhile, a lens-fitted photo film unit having a flash deviceincorporated therein is widely known. Since the flash device for thelens-fitted photo film unit is required to be inexpensive and compact,the flash switch is constituted of a metal blade and contact chipsformed on a flash circuit board such that the metal blade is broughtinto contact with the contact chips through a manual operation member,to close the flash circuit and thus cause the flash circuit to startcharging. Conventionally, the manual operation member is a push buttonor a sliding button. Some of the conventional manual operation membersare provided with a fastening mechanism by which the metal blade is keptin contact with the contact chips once the operation member is operatedfor a moment. Others are designed to bring the metal blade into contactwith the contact chips only while the photographer operates the manualoperation member.

The flash device of the lens-fitted photo film unit has been providedwith a light emission element for indicating completion of charging theflash device. In the conventional lens-fitted photo film unit, the lightemission element is placed behind an indication window formed through arear wall of the lens-fitted photo film unit, or is placed in connectionto a light guide that conducts light from the light emission element toa view field of a viewfinder.

Where the charge switch operation device is provided with the fasteningdevice, the flash device keeps charging so long as the operation deviceis in the ON position. If the operation device is left in the chargingposition after the photography is terminated, the battery is wasted. Asa result, the battery runs down and it becomes impossible to use theflash device before all of the available exposures are carried out. Suchtrouble will be prevented if only the photographer checks the positionof the operation member or the light from the light emission element atthe conclusion of photography. However, according to the configurationsof the conventional lens-fitted photo film units, it is not easy to knowthe switching condition of the operation member at a glance, or thecharge condition indicating light is not visible from the outside of thelens-fitted photo film unit. Therefore, the photographer can fail toreset the charge switch to the OFF position.

In view of the foregoing, a prime object of the present invention is toprovide an autostop flash device which cuts the cost and space withoutlowering reliability and stability.

A further object of the present invention is to provide a flash devicewhich is effective to prevent the photographer from forgetting to turnoff the flash charge switch, and is also suitable especially for use ina lens-fitted photo film unit.

DISCLOSURE OF THE INVENTION

In a flash device comprising an oscillation circuit that startsoscillating when a flash charge switch is turned on, wherein theoscillation circuit is comprised of an oscillation transformer having aprimary coil connected to a power source and a secondary coil connectedto a main capacitor, and the secondary coil is inductively coupled tothe primary coil such that a high voltage current is induced in thesecondary coil while the oscillation circuit oscillates, and that themain capacitor is charged with the high voltage current up to a setcharge voltage,

the present invention is comprised of a tap point located at anintermediate position of the secondary coil, the tap point having apotential that changes proportionally to the charge voltage across themain capacitor; a Zener diode connected to the tap point, to conduct aZener current when the potential at the tap point reaches a value thatcorresponds to the set charge voltage of the main capacitor; and astopping transistor activated by the Zener current to stop theoscillation circuit from oscillating and thus stop charging the maincapacitor when the main capacitor reaches the set charge voltage.

The flash device according to the invention makes it possible to use aninexpensive Zener diode with a low Zener voltage, so that it is possibleto cut the cost of the flash device.

By charging a stopping capacitor with the Zener current that flows whenthe main capacitor reaches the set charge voltage and then applyingcurrent discharged from the stopping capacitor to the stoppingtransistor through a resistor, the stopping transistor keeps operatingfor a predetermined time. It ensures stopping charging the maincapacitor, and also prevents unexpected interruption of charging thatmay be caused by noises.

Moreover, a temperature coefficient of a forward voltage of a rectifyingdiode that blocks current flowing from the tap point to the Zener diodeshould have an opposite polarity to a temperature coefficient of theZener voltage of the Zener diode, such that the Zener diode and therectifying diode form a mutual temperature compensating circuit.Thereby, the main capacitor is charged up to the constant set voltagewithout being affected by environmental temperature or the like.

To achieve the second object in a flash device comprising a flashcircuit and a flash charge switch for charging the flash circuit, thepresent invention is characterized by comprising an indication devicefor indicating completion of charging the flash circuit, the indicationdevice protruding outside when the flash charge switch is turned on.

As the indication device for indicating the completion of charging theflash circuit protrudes outside when the flash charge switch is turnedon, it is easy to check if the flash charge switch is in the ON state ornot. Accordingly, the present invention is effective to remind thephotographer to turn off the charge switch when the flash circuit needsnot charging. Thus, the flash device of the present invention solves theabove described problem of wasting the battery and making the flashdevice useless for the following photography.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a lens-fitted photo film unit with aflash device according to a first embodiment of the invention;

FIG. 2 is a circuit diagram of the flash device of the first embodimentof the invention;

FIGS. 3A and 3B are timing charts illustrating the operation of theflash device of the first embodiment;

FIG. 4 is a perspective view of a lens-fitted film unit with a flashdevice according to a second embodiment of the invention;

FIG. 5 is a circuit diagram of the flash device according to the secondembodiment of the invention;

FIG. 6 is a signal chart illustrating the charging operation of theflash device of the second embodiment;

FIG. 7 is a perspective view of a lens-fitted photo film unit with aflash device according to a third embodiment of the invention, in astate where the flash device is not used;

FIG. 8 is a perspective view of the lens-fitted photo film unit of FIG.7 in a state where the flash device is used;

FIG. 9 is an exploded perspective view of the lens-fitted photo filmunit of FIG. 7;

FIG. 10 is an exploded perspective view of a front cover of thelens-fitted photo film unit of FIG. 7;

FIG. 11 is a circuit diagram of the flash device of the thirdembodiment;

FIG. 12 is an exploded perspective view of an indication device forindicating completion of charging the flash device of the thirdembodiment and its mounting condition;

FIG. 13 is a perspective view of the other side of the indication deviceof FIG. 12;

FIG. 14 is a sectional view illustrating the indication device of FIG.12 in the state where the flash device is not used;

FIG. 15 is a sectional view illustrating the indication device of FIG.12 in the state where the flash device is used;

FIG. 16 is a perspective view illustrating a second example of lightguide portion of the indication device;

FIG. 17 is a perspective view illustrating a third example of lightguide portion;

FIG. 18 is a perspective view illustrating a fourth example of lightguide portion;

FIG. 19 is a perspective view illustrating a fifth example of lightguide portion;

FIG. 20 is a perspective view illustrating a sixth example of lightguide portion;

FIG. 21 is a sectional view of essential parts of acompletion-of-charging indication device that does not use a lightguide, in a state where the flash device is not used;

FIG. 22 is a sectional view of essential parts of thecompletion-of-charging indication device of FIG. 21 in a state where theflash device is used;

FIG. 23 is a circuit diagram of another embodiment of flash circuit; and

FIG. 24 is a circuit diagram of a conventional flash circuit.

PREFERRED EMBODIMENT OF THE INVENTION

The present invention will be described in more detail with reference tothe accompanying drawings.

Referring to FIG. 1, a lens-fitted photo film unit 10, hereinafterreferred to as a film unit, has a unit body 11 containing a photofilmstrip. A simple photographic mechanism and a flash device areincorporated into the unit body 11. A decorative cardboard paper 12 iswrapped around the unit body 11. A taking lens 13, a finder objectivewindow 14, a frame counter window 15, a film winding wheel 16, a flashprojector 17, a shutter button 18, a charging operation member or chargebutton 19 and other necessary elements are exposed to the outsidethrough openings of the cardboard paper 12 or located out of thecardboard paper 12. An indication window for indicating that the flashdevice is ready to flash is formed besides a viewfinder eyepiece,through they are not shown in the drawings.

Referring to FIG. 2 showing a flash circuit of the flash device, a flashcharge switch 26 is turned on so long as the charge button 19 isdepressed. Once the flash charge switch 26 is turned on for a moment bydepressing the charge button 19, the flash circuit continues to charge amain capacitor 41 up to a set charge voltage even after the flash chargeswitch 26 is turned off as the photographer quits depressing the chargebutton 19. Once the main capacitor 41 is charged up to the set voltage,the main capacitor 41 is automatically repeatedly charged up to the setvoltage immediately after each flashing.

The flash circuit roughly consists of a booster section 20 and acharging-discharging section 40. The booster section 20 is mainlyconstituted of a battery 21 of 1.5V as a power source, an oscillationtransistor 22 of NPN type, an oscillation transformer 23, a latchingtransistor 24 of PNP type, a charge current rectifying diode 25, theflash charge switch 26, a recharging capacitor 27 and an oscillationstopping circuit 35.

The oscillation transformer 23 is constituted of a primary coil 31,secondary coil 32 and a tertiary coil 33 which are inductively coupledto one another. In the oscillation transformer 23, terminals of theprimary coil 23 are referred to as first and second terminals 23 a and23 b, one terminal of the tertiary coil 33 is referred to as a thirdterminal 23 c, another terminal of the tertiary coil 33, which is alsoone terminal of the secondary coil 32, is referred to as a fourthterminal 23 d, and another terminal of the second coil 32 is referred toas a fifth terminal 23 e. The oscillation transformer 23 has a tap point23 f at an intermediate position of a secondary coil 32, in addition tothe first to fifth terminals 23 a to 23 e.

The first and second terminals 23 a and 23 b of the oscillationtransformer 23 are connected to the collector of the oscillationtransistor 22, and the plus pole of the battery 21, respectively. Thethird terminal 23 c is connected to the plus terminal of the battery 21through a resistor 34 a and the flash charge switch 26. The fourthterminal 23 d is connected to the base of the oscillation transistor 22,and the fifth terminal 23 e is connected through the charge currentrectifying diode 25 to the negative side of the charging-dischargingsection 40, that is, the minus terminal of the main capacitor 41. Thecathode of the charge current rectifying diode 25 is connected to thefifth terminal 23 e. The emitter of the oscillation transistor 22 isconnected to the minus pole of the battery 21 and is grounded.

The oscillation transistor 22 and the oscillation transformer 23constitute a well-known blocking oscillator that transforms the lowvoltage of the battery 21 to the high voltage for charging the maincapacitor 41. The oscillation transistor 22 is activated to conduct itscollector current to the primary coil 31 when the flash charge switch 26is turned on. As the base current of the oscillation transistor 22increases due to the positive feedback from the oscillation transformer23, its collector current increases, and thus the oscillation transistor22 oscillates.

While the oscillation transistor 22 oscillates, a high voltage, e.g. analternating voltage of about 1000V, is generated in accordance with theturn ratio of the primary coil 31 to the secondary coil 32. The chargecurrent rectifying diode 25 supplies the charging-discharging section 40with only those secondary current flowing through the secondary coil 32in a direction from the fifth terminal 23 e to the fourth terminal 23 d.

The latching transistor 24 applies a bias voltage to the base of theoscillation transistor 22 after the flash charging switch 26 is turnedoff, thereby to keep the oscillation transistor 22 oscillating. Thelatching transistor 24 is connected at its emitter to the plus pole ofthe battery 21, at its base to the collector of the oscillationtransistor 22 through a resistor 34 b, and at its collector to the baseof the oscillation transistor 22 through the resistor 34 a and thetertiary coil 33.

In this way, the latching transistor 24 is turned on in response to theactivation of the oscillation transistor 22, so that the oscillationtransistor 22 continues to oscillate even after the flash charge switch26 is turned off, because of positive feedback from the latchingtransistor 24. It is possible to omit the latching transistor 24.

When a back electromotive force is generated in the tertiary coil 33while the flash charging switch 26 is off, if there is no current loopor runaway for the back electromotive force, the oscillation of theblocking oscillator would not be stable, or it would take longer time tocharge up the main capacitor 41. To avoid this problem, a looping diode28 is provided. Anode of the looping diode 28 is connected through theresistor 34 a to the third terminal 23 c of the tertiary coil 33, andcathode thereof is connected to the plus pole of the battery 21, therebyforming a current loop for the back electromotive force on the tertiarycoil 33.

The charging-discharging section 40 is constituted of the main capacitor41, a flash discharge tube 42, a triggering electrode 42 a, a neon lamp43, a triggering capacitor 44, a triggering transformer 45, a triggeringswitch 46 and so forth. The main capacitor 41 is connected in parallelto the flash discharge tube 42. The positive terminal of the maincapacitor 41 is also connected to the minus pole of the battery 21 andthus grounded. The negative terminal of the main capacitor 41 isconnected to anode of the charge current rectifying diode 25. The setcharge voltage of the main capacitor 41 is 300V in the presentembodiment, so the flash discharge tube 42 is designed to flash light ofa predetermined amount when the voltage of 300V is applied to it. Sincethe positive terminal of the main capacitor 41 is connected to the minuspole of the battery 21, the potential at the positive terminal of themain capacitor 41 is maintained to be the ground potential GND (=0V), sothe potential at the negative terminal of the main capacitor 41 lowerswith the charging. That is, the charge voltage is an absolute value thatis equal to a potential difference between the positive and negativeterminals of the main capacitor 41.

According to the second embodiment, an oscillation stopping circuit 35is mainly constituted of a rectifying diode 36, a Zener diode 37 and astopping transistor 38. The cathode of the rectifying diode 36 isconnected to the tap point 23 f, and the anode of the rectifying diode36 is connected to the anode of the Zener diode 37 through a resistor 36a. The rectifying diode 36 is provided for rectifying the oscillating oralternating voltage at the tap point 23 f, and tapping out only negativehalves of the alternating voltage. The rectifying diode 36 alsofunctions as a temperature compensating element for the Zener diode 37,as set force in detail later. A capacitor 39 is provided for smoothingthe voltage from the rectifying diode 36, and applying it as a DCvoltage to the Zener diode 37. The stopping transistor 38 has the baseconnected to the cathode of the Zener diode 37 through a resistor 37 a,the emitter connected to the fourth terminal 23 d of the oscillationtransformer 23, and the collector grounded.

The potential level Va at the tap point 23 f varies alternately incorrespondence with the oscillation of the oscillation transformer 23.Beside that, the potential level Va in total changes proportionally tothe charge voltage in the main capacitor 41. Since the main capacitor 41is charged in the negative direction, so the potential Va at the tappoint 23 f goes down proportionally as the charge voltage increases. Thetap point 23 f is located such that a potential difference or voltage“Vb−Va” between the fourth terminal 23 d and the tap point 23 f comes toa given voltage Von while an electromotive force is generated in thesecondary coil 32 after the main capacitor 41 is charged up to a setcharge voltage, e.g. 300V. More specifically, the tap point 23 f islocated such that the DC voltage applied across the Zener diode 37reaches a Zener voltage Vz of the Zener diode 37 when the charge voltageacross the main capacitor 41 reaches the set value.

The voltage Von is given by adding a voltage drop amount through therectifying diode 36, e.g. about 0.6V, to a Zener voltage Vz, e.g. 10V,of the Zener diode 37. In this instance, the given voltage Von is 10.6V,and the tap point 23 f is located where the turn number between the tappoint 23 f and the fourth terminal 23 d is about {fraction (1/30+L )}the total turn number of the secondary coil 32. However, if the Zenervoltage Vz of the Zener diode 37 is 30V, the voltage Von is given as30.6V, and the tap point 23 f is located where the turn number betweenthe tap point 23 f and the fourth terminal 23 d is about {fraction(1/10)} the total turn number of the secondary coil 32.

According to the above circuit construction, the Zener diode 37 issupplied with the DC voltage which is obtained through the rectifyingdiode 36 and the smoothing capacitor 39 from the alternating voltagebetween the fourth terminal 23 d and the tap point 23 f, i.e. from thepotential difference Vb−Va. Accordingly, the Zener voltage Vz of theZener diode 37 may be low, e.g. 10V, so that an inexpensive Zener diodemay be used as the Zener diode 37. When the main capacitor is charged upto the set voltage of 300V, the potential difference Vb−Va reaches thegiven value Von, and thus the Zener voltage Vz is applied across theZener diode 37. Then, the Zener diode 37 conducts a Zener current of theopposite direction to the charging current.

Unless the Zener diode 37 conducts the Zener current, no current flowsin the base of the stopping transistor 38, so that the stoppingtransistor 38 is in the OFF state. When the Zener diode 37 conducts theZener current, i.e. when the cathode potential of the Zener diode 37goes below 0V, a voltage higher than an activation voltage for thestopping transistor 38 is applied across the emitter-base circuit of thestopping transistor 38, so the stopping transistor 38 is turned on. Whenthe stopping transistor 38 is turned on, the base and the emitter of theoscillation transistor 22 are connected to each other to have the samepotential level, so that the oscillation transistor 22 is turned off,and thus the latching transistor 24 is turned off.

Because the turn ratio of the coil portion between the tap point 23 fand the fourth terminal 23 d to the primary coil 31 is remarkablysmaller than the turn ratio of the entire secondary coil 32 to theprimary coil 31, it is possible to tap out a comparatively large currentfrom the tap point 23 f. Therefore, even when the voltage from thebattery 21 is lowered, for example due to a low ambient temperature, asufficiently large base current enough for activating the stoppingtransistor 38 may be supplied to the base of the stopping transistor 38.Thus, the reliability of automatic stopping of the oscillationtransistor 22 is improved.

As well-known in the art, the conductivity of semiconductor elementsvaries depending upon their temperatures. Concerning Zener diodes, theZener voltage increases or decreases with a temperature increasedepending upon a set Zener voltage that is determined under a referencetemperature. Specifically, those Zener diodes whose set Zener voltage isless than 5 to 6 volts have a negative temperature coefficient each, sothe actual Zener voltage decreases with the temperature increase. On thecontrary, those Zener diodes whose set Zener voltage is more than 5 to 6volts have a positive temperature coefficient each, so the actual Zenervoltage increases with the temperature increase.

The Zener voltage Vz also varies according to the variation incircumferential temperature as well as the temperature change due toheat in the Zener diode 37. As the Zener voltage Vz is set to be 10V inthis instance, the Zener diode 37 has a positive temperaturecoefficient, so the actual Zener voltage Vz goes up as the temperaturegoes up. Without any temperature compensation, the Zener diode 37 wouldstart conducting the Zener current when the voltage Vb−Va goes up abovethe given voltage Von, i.e. until the main capacitor 41 has been chargedup to a value more than the set value.

However, those diodes which are used for rectifying have negativetemperature coefficients. Therefore, as the temperature increases, thevoltage drop through the rectifying diode 36 decreases, and thus thevoltage applied to the Zener diode 37 increases. Therefore, the negativetemperature coefficient of the rectifying diode 36 is designed tocompensate for the positive temperature coefficient of the Zener diode37. That is, the total temperature coefficient of the diodes 36 and 37is approximately zero. In this way, the Zener current begins to flow atthe set charge voltage of the main capacitor 41, regardless of thetemperature variations.

The current from the booster section 20 is charged in the main andtriggering capacitors 41 and 44. When the main capacitor 41 is chargedup to its set charge voltage of 300V, the neon lamp 43 starts lighting.The light from the neon lamp 43 is conducted through a not-shown lightguide or the like to the indication window near the eyepiece, so thatthe photographer can see that the flash device is ready to flash.

The trigger switch 46 is turned on when a shutter blade is opened up.Then, the triggering capacitor 44 discharges current to a primary coil45 a of the triggering transformer 45. As a result, a high voltagetrigger voltage, e.g. 4KV, is induced in a secondary coil 45 b of thetransformer 45, which is applied to the triggering electrode 42 a. Thehigh voltage ionizes Xenon gas in the flash discharge tube 42 to breakthe resistance between its electrodes, so that the main capacitor 41discharges, causing the flash discharge tube 42 to flash.

The recharging capacitor 27 of the booster section 20 is charged withthe secondary current of the secondary coil 32, in the same way as themain capacitor 41. The charge loaded in the recharging capacitor 27 isdischarged when the flash discharge tube 42 flashes, and flows into thebase of the oscillation transistor 22, so that the oscillationtransistor 22 is turned on to restart charging the main capacitor 41.

Now, the operation of the above described embodiment will be described.First the photographer rotates the film winding wheel 16 of the filmunit 10 to wind up the filmstrip by one frame and also cock the shutter.If a flash photography is needed, the charge button 19 is depressed toturn on the flash charge switch 26. The photographer can quit depressingthe charge button 19 as soon as it is fully depressed.

When the flash charge switch 26 is turned on, the base current isapplied to the oscillation transistor 22 through the resistor 34 a andthe tertiary coil 33. Thereby, the oscillation transistor 22 isactivated to conduct the collector current as much as the base current.As the collector current flows from the second terminal 23 b through theprimary coil 31 to the first terminal 23 a, the collector current isequal to the primary current.

Because of the primary current, the electromotive force of the highvoltage is generated in the secondary coil 32, so that the secondarycurrent flows from the fifth terminal 23 e to the fourth terminal 23 d.The secondary current flows into the base of the oscillation transistor22, so that the base current increases. As the base current increases,the collector current, i.e. the primary current through the primary coil31 increases.

When the oscillation transistor 22 is turned on, the current flowing tothe collector of the oscillation transistor 22 is also applied to thebase of the latching transistor 24, so that the latching transistor 24is turned on. Then, the voltage of the battery 21 begins to be appliedto the base of the oscillation transistor 22 through the resistor 34 aand the tertiary coil 33.

Because of the positive feedback from the oscillation transformer 23,the base current of the oscillation transistor 22 and the collectorcurrent of the oscillation transistor 22 increase concurrently. But asthe oscillation transistor 22 is being saturated, the collector currentis getting less increase. Thereby, the change in the primary currentbecomes smaller, and back electromotive forces are generated in therespective coils 31 to 33 of the oscillation transformer 23. Due to theback electromotive force, the current flowing from the secondary coil 32to the base of the oscillation transistor 22 drops down. Thus, thecollector current of the oscillation transistor 22 drops down.

However, because the latching transistor 24 applies the base voltage ofthe oscillation transistor 22, the oscillation transistor 22 is notcompletely turned off. After the back electromotive force on theoscillation transformer 23 stops, the base voltage from the latchingtransistor 24 causes the collector current of the oscillation transistor22 to increase again. Accordingly, the primary current begins toincrease again. In this way, even after the flash charge switch 26 isturned off, the oscillation transistor 22 or the blocking oscillatorcontinues to oscillate.

The secondary current is generated by the electromotive force of thehigh voltage induced in the secondary coil 32 during the oscillation.Among the secondary current, those flowing in the direction from thefifth terminal 23 e to the fourth terminal 23 d are supplied through thecharge current rectifying diode 25 to the charging-discharging section40, and is charged in the main capacitor 41 and the triggering capacitor44. Simultaneously, the recharging capacitor 27 is charged with thissecondary current.

On the assumption that the ground potential GND at the minus pole of thebattery 21 is a reference level (=0V), the potential level Vb at thefourth terminal 23 d is maintained at a constant level that is higherthan the ground potential GND by the base-emitter voltage of theoscillation transistor 22 while the electromotive force is generated onthe oscillation transformer 23 in the first stage of charging when thecharge voltage is around 0V, as shown in FIG. 5A. While the backelectromotive force is generated, the potential level Vb at the fourthterminal 23 d drops down like a pulse.

The potential level Va at the tap point 23 f is maintained constantwhile the electromotive force is generated, and jumps up like a pulsewhile the back electromotive force is generated. In either phase, thepotential level Va is higher than the potential level Vb at the fourthterminal 23 d. Therefore, in the first stage of charging, the potentialdifference Vb−Va is applied across the rectifying diode 36 in theopposite direction, so that no current flows to the Zener diode 37 andthus to the base of the stopping transistor 38, so the stoppingtransistor 38 is not turned on.

As the main capacitor 41 is charged, the voltage across the maincapacitor 41 increases. In this embodiment, the main capacitor 41 isdesigned to be charged in the negative direction, the positive terminalof the main capacitor 41 is maintained 0V, and the potential level atthe negative terminal of the main capacitor 41 goes down. As a result,the load on the secondary coil 32 increases, so that the secondarycurrent decreases, and the voltage of the electromotive force and thatof the back electromotive force on the secondary coil 32 go down. Inaddition, the oscillation frequency of the blocking oscillator goes up.

As the cycle of change in the potential level Va is getting shorter, thepotential level Va goes down as the whole. On the other hand, thepotential level Vb at fourth terminal 23 d changes between the samelevels as in the first stage of charging, even through the cycle ofchange is getting shorter in the same way as the potential level Va.Consequently, the potential level Va goes below the potential level Vbwhile the electromotive force is generated, so that the voltage startsto be applied across the Zener diode 37. However, until the chargevoltage of the main capacitor reaches the set value, the potentialdifference Vb−Va is less than the given voltage Von, so the voltageapplied to the Zener diode 37 is less than the Zener voltage Vz.Therefore, the Zener diode 37 does not conduct the Zener current, andthe stopping transistor 38 is not turned on until the main capacitor 41is charged up to the set charge voltage. In this way, the oscillationtransistor 22 continues to oscillate until the main capacitor 41 ischarge up to the set charge voltage.

When the main capacitor 41 is charged up to the set voltage, i.e. 300Vin this embodiment, the potential difference or voltage Vb−Va comes tothe given voltage Von, i.e. 10.6V, as shown in FIG. 3B, while theelectromotive force is generated. Then, the Zener voltage Vz is appliedacross the Zener diode 37 through the rectifying diode 36, so that theZener current flows through the Zener diode 37. Because of the Zenercurrent, a current flows from the fourth terminal 23 d to the base ofthe stopping transistor 38, turning on the stopping transistor 38.Indeed the voltage Vb−Va varies according to the oscillation of theblocking oscillator, it is rectified and smoothed through the rectifyingdiode 36 and the smoothing capacitor 39 before being applied to theZener diode 37, it is possible to stably turn on the stopping transistor38.

When the stopping transistor 38 is turned on, the base of theoscillation transistor 22 is connected to the emitter thereof throughthe stopping transistor 38, so that the oscillation transistor 22 isturned off. When the oscillation transistor 22 is turned off, the basecurrent of the latching transistor 24 stops, so that the latchingtransistor 24 is turned off. Then, the oscillation transistor 22 doesnot continue to oscillate, thereby stopping charging the main capacitor41. When the charging stops, the stopping transistor 38 is turned off.Even when the stopping transistor 38 is turned off, the oscillationtransistor 22 cannot restart oscillating.

Beside that, the neon lamp 43 starts lighting when the main capacitor 41is charged up to the set voltage, so the photographer can see that theflash device is ready to flash. Then, the photographer can depress theshutter button 18 to make the flash photography while framing throughthe viewfinder.

When the shutter button 18 is depressed, the shutter is activated, andthe triggering switch 46 is turned on the moment the shutter is fullyopened. Upon the triggering switch 46 being turned on, the triggeringcapacitor 44 discharges, so that the current flows through the primarycoil 45 a of the triggering transformer 45, inducing the triggeringvoltage across the secondary coil 45 b. The triggering voltage isapplied through the triggering electrode 42 a to the flash dischargetube 42. Then, the main capacitor 41 is discharged through the flashdischarge tube 42, causing the flash discharge tube 42 to flash. Thenthe flash projector 17 projects light to accomplish the flashphotography.

Because of the mutual temperature compensation effect of the Zener diode37 and the rectifying diode 36, the main capacitor 41 is charged up tothe set voltage without any variation in the charge voltage. Therefore,the flash photography is always carried out with an approximatelyconstant amount of flashlight.

Simultaneously with the flash discharge tube 42 emits light, therecharging capacitor 27 is discharged through the flash discharge tube42. The discharged current from the recharging capacitor 27 flows intothe base of the oscillation transistor 22. Thereby, the oscillationtransistor 22 is reactivated. When the oscillation transistor 22 isreactivated, the latching transistor 24 is turned on just like when theflash charge switch 26 is turned on for a moment. The latchingtransistor 24 makes the oscillation transistor 22 continue oscillating.In this way, the main capacitor 41 restarts being charged.

Now a flash circuit according to a second embodiment will be described,whose fundamental configurations are equivalent to those of the firstembodiment, wherein like reference numerals designate like orcorresponding parts. The following description merely relates to thoseportions essential to the second embodiment.

A film unit 10 shown in FIG. 4 is provided with a charging operationmember 50 that is slidable between an ON position and an OFF position.Setting the charging operation member 50 in the ON position causes aflash device to start charging a main capacitor 41 up to a set voltage,e.g. 300V. So long as the charging operation member 50 is maintained inthe ON position, the main capacitor 41 is intermittently charged up tothe set voltage for supplement natural discharge. The charging operationmember 50 is also used for selecting whether a flash light is to beprojected or not. That is, when the charging operation member 50 is inthe ON position, the flash light is projected during the exposure. Butwhen the charging operation member 50 is in the OFF position, the flashlight is not projected even if the main capacitor 41 is fully charged.

FIG. 5 shows the flash circuit provided in the film unit of FIG. 10. Abooster section 20 is provided with a flash charge switch 51 that isturned on while the charging operation member 50 is in the ON position,or off while the charging operation member 50 is in the OFF position.Unlike the above embodiments, the booster section 20 does not have alatching transistor 24, a looping diode 28, a recharging capacitor 27and a smoothing capacitor 39. When the flash charge switch 51 is turnedon, a current flows into the base of an oscillation transistor 22, sothat the oscillation transistor 22 oscillates, and the main capacitor 41is charged with a high voltage generated through an oscillationtransformer 23. That is, a blocking oscillator consisting of theoscillation transistor 22 and the oscillation transformer 23 operateswhile the flash charge switch 51 is in the ON state.

Instead of a neon lamp, a light emission diode (LED) 52 is connectedbetween a third terminal 23 c and a fourth terminal 23 d of theoscillation transformer 23, for indicating completion of charging of themain capacitor 41. Anode of the LED 52 is connected to the fourthterminal 23d such that the LED 52 starts lighting when the maincapacitor 41 is charged up to the set voltage. Detail of the LED 52 isdisclosed in JPA 8-115796.

An oscillation stopping circuit 55 includes a rectifying diode 36connected in series to a tap point 23 f of a secondary coil 32,resistors 36 a and 37 a, a Zener diode 37 and a stopping transistor 38,in the same way as the above embodiment, but also includes a stoppingcapacitor 53. Also in this embodiment, the rectifying diode 36 and theZener diode 37 constitute a mutual temperature compensating circuit.

Since the flash charge switch 51 is maintained in the ON state when tocharge the main capacitor 41, if the stopping transistor 38 is turned ononly for a short time, the oscillation transistor 22 cannot always bedeactivated. To make sure that the oscillation transistor 22 stopsoscillating when the main capacitor 41 is charged up to the set voltage,the stopping capacitor 53 is connected directly between cathode of theZener diode 37 and the fourth terminal 23 d of the oscillationtransformer 23. When the main capacitor 41 is charged up to the setvoltage, a Zener current flows through the Zener diode 37, in the sameway as described with respect to the second embodiment of FIG. 4. Butthe Zener current flows through the stopping capacitor 53 in thedirection from the fourth terminal 23 d to the tap point 23 f, so thatthe stopping capacitor 53 is charged with the Zener current directly,that is, without any intermediate resistor. Therefore, the stoppingcapacitor 53 is charged up to an appropriate full voltage in a moment,e.g. about 10 ms (micro seconds).

As shown in FIG. 6, as the Zener current flows through the stoppingcapacitor 53 immediately after the charge voltage of the main capacitor41 reaches the set value, the base-emitter voltage of the stoppingtransistor 38 comes to zero volt, so that the stopping transistor 38 isnot turned on. When the stopping capacitor 53 is charged up, the chargevoltage of the stopping capacitor 53 is applied across the base-emittercircuit of the stopping transistor 38, so that the circuit from thestopping capacitor 53 through the base and the emitter of the stoppingtransistor 38 to the resistor 37 a is closed, and thus the stoppingcapacitor 53 discharges. The discharged current flows in the base of thestopping transistor 38, thereby turning on the stopping transistor 38.As a result, a current that has been applied from a battery 21 to thebase of the oscillation transistor 22 through the flash charge switch 51begins to flow through the emitter-collector circuit of the stoppingtransistor 38, so that the oscillation transistor 22 is deactivated, andthe charging the main capacitor 41 is terminated.

Discharging through the resistor 37 a is for supplying the base currentof the stopping transistor 38 for a longer time. As long as the basecurrent is supplied, the stopping transistor 38 is turned on.Consequently, the stopping transistor 38 is turned on for the longertime enough to stop the oscillation transistor 22 from oscillating. TheON-period of the stopping transistor 38 may be set by adjusting timecoefficient that is determined by the capacitance of the stoppingcapacitor 53 and the resistance of the resistor 37 a. In thisembodiment, the capacitance of the stopping capacitor 53 is 47 μF, andthe resistance of the resistor 37 a is 10 KΩ, whereby the ON-period ofthe stopping transistor 38 is set to be 0.3 seconds in actualmeasurement. According to this configuration, the oscillation transistor22 stops oscillating at least for 0.3 seconds, even while the flashcharge switch 51 is in the ON state.

As the stopping capacitor 53 discharges, the charge voltage of thestopping capacitor 53 goes down. When the charge voltage of the stoppingcapacitor 53 goes below a predetermined value, the stopping transistor38 is turned off. So long as the flash charge switch 51 is in the ONstate, the current from the battery 21 restarts flowing into the base ofthe oscillation transistor 22, so that the oscillation transistor 22restarts oscillating. Since the main capacitor 41 has already beencharged up to the set voltage, the Zener current flows through the Zenerdiode 37 as soon as the oscillation restarts. As the stopping capacitor53 is charged with the Zener current soon to the full and then startsdischarging, the stopping transistor 38 is turned on by the dischargedcurrent in short time after the restart of oscillation. Thus, chargingthe main capacitor 41 is terminated soon.

In the same way as above, the stopping transistor 38 is turned on andoff repeatedly, so that the oscillation transistor 22 stops and restartsoscillating repeatedly. Therefore, so long as the flash charge switch 51is in the ON state, the main capacitor 41 is charged repeatedly andintermittently to supplement the natural discharge of the main capacitor41, and thereby to maintain the charge voltage of the main capacitor 41approximately constant.

In a charging-discharging section 40, a terminal of a triggeringcapacitor 44 and a common terminal of primary and secondary coils 45 aand 45 b are connected to a pulse pole of the battery 21, and a flashselection switch 54 is connected in series to the triggering capacitor44. The flash selection switch 54 is turned on or off in cooperationwith the flash charge switch 51 being turned on or off by setting thecharging operation member 50 to the ON position, or to the OFF position,respectively.

According to this configuration, when the flash selection switch 54 isin the ON state, the triggering capacitor 44 is charged with the currentfrom the booster section 20, and is discharged upon a triggering switch46 being turned on. Then a triggering voltage is applied to a flashdischarge tube 42. Even while the main capacitor 41 is fully charged, ifthe flash selection switch 54 is in the OFF state, the triggeringcapacitor 44 could not discharge, so that no flash light is projected.

As the main capacitor 41 is being charged, the potential at the thirdterminal 23 c goes down gradually. Finally, the potential at the thirdterminal 23 c becomes less than the potential at the fourth terminal 23d in the phases when back electromotive forces are not generated. Then,the voltage is applied across the LED 52 in its forward direction. Inthis embodiment, when the charge voltage in the main capacitor 41 goesabove 250V, the potential difference between the third and fourthterminals 23 c and 23 d becomes so large that the LED 52 emits light ata visible intensity. When the main capacitor 41 is charged up to the setvoltage of 300V, the potential difference between the third and fourthterminals 23 c and 23 d becomes large enough for the LED 52 to emitlight at a predetermined high intensity.

The LED 52 stops lighting while the stopping transistor 38 is turned on.Therefore, the intermission interval of the LED 52 is defined at thesame time as the ON-period of the stopping transistor 38 is defined byadjusting the time coefficient that is determined by the capacitance ofthe stopping capacitor 53 and the resistance of the resistor 37 a. If,for example, an LED is provided in a flash circuit where a stoppingtransistor is turned on directly by the Zener current, the intervals ofintermission of lighting of the LED could vary largely due to variationsin the circumferential temperature, in the leak current from a maincapacitor, in the performance of the individual Zener diode, and so on.According to the configuration of FIG. 5, the LED 52 can emit light atregular intervals.

It is possible to provide the same stopping capacitor as above in theflash circuit of FIG. 2 between the cathode of the Zener diode 37 andthe fourth terminal 23 d. Thereby, the stopping transistor 38 will notbe affected by electric noises that might be caused when the maincapacitor 41 is almost charged up to the set voltage, and will be turnedon for a sufficiently long time enough to stop charging the maincapacitor 41.

The oscillation stopping circuit 55 using the stopping capacitor 53 ispreferably applicable to a flash circuit which needs to keep pushing acharge button to continue charging. Although the above describedembodiments charge the main capacitor in the negative direction, thepresent invention is applicable to those flash circuits whose maincapacitor is charged in the positive direction. In that case, thepotential of a tap point at an intermediate position of a secondary coilof an oscillation transformer increases as the charge voltage in themain capacitor increases. Accordingly, a rectifying diode and a Zenerdiode should be connected in the opposite polarity to the aboveembodiments between the tap point and the base of a stopping transistor.

In those types of flash device where the flash device repeats chargingso long as the flash charge switch is turned on, like the embodimentshown in FIG. 4, if the photographer inadvertently leave the chargingoperation member in the ON position, the battery can run down and theflash photography becomes impossible before all of the available pictureframes have been photographed. This will be prevented if only thephotographer checks the position of the charging operation member or theindication light for indicating completion of charging, at theconclusion of photography. However, where the switching condition of thecharging operation member is not apparent or the indication lightindicating the completion of charging is not conspicuous, thephotographer can fail to reset the charging operation device to the OFFposition. This trouble is more likely to occur when the photographer isunfamiliar with the film unit. The following embodiment is effective toprevent the photographer from forgetting to turn off the flash chargeswitch.

FIG. 7 shows an outer appearance of the film unit 10 in a conditionwhere no flash light is projected. In a front side of the film unit 10,there are a taking lens 13, a finder objective window 14, a flashprojector 17, a charging operation member 56, and a view changing knob57. On a top side of the film unit 10, there are a shutter button 18, aframe counter window 15, and an opening 61 through which a chargecondition indicator 60 can come out as shown in FIG. 8. On a rear sideof the film unit 10, there are a film winding wheel 16, a findereyepiece window 14 c and other elements, as shown in FIG. 9.

The charging operation member 56 is slidable in a vertical directionbetween an OFF position shown in FIG. 7 and an ON position shown in FIG.8. The charging operation member 56 is slid up to the ON position forcharging a built-in flash device 70, or down to the OFF position for notcharging the flash device 70. When the charging operation member 56 isset to the ON position, the charge condition indicator 60 pops upthrough the opening 61 as shown in FIG. 8. The charge conditionindicator 60 starts lighting when the flash device 70 completescharging. The view changing knob 57 is provided below the taking lens 13so as to be slidable along an arcuate slot 58 around the taking lens 13.

As shown in FIG. 9, the unit main body 3 is constituted of a basicportion 68 containing a photo film cartridge 67, an exposure unit 69 andthe flash device 70, which are attached to the front of the basicportion 68, a front cover 71 covering the front of the basic portion 68,and a rear cover 71 covering the rear of the basic portion 68. Thesecomponents are assembled by snap-in engagement.

The basic portion 68 has an exposure chamber .74 in its center portion,and a cartridge chamber 75 and a film roll chamber 76 holdingrespectively a cartridge shell 66 and a roll of unexposed filmstrip 65on opposite sides of the exposure chamber 74, which are formed as anintegral body. The exposure chamber 74 has an exposure aperture 74 adefining a frame exposure range on the filmstrip 65. In this embodiment,the film cartridge 67 is of IX240 type, so the frame exposure range isof a high-vision size (aspect ratio 1.8).

The rear cover 72 closes the cartridge chamber 75 and the film rollchamber 76 from the rear side, and bottom lids 78 and 79 formedintegrally with the rear cover 71 close bottoms of the chambers 75 and76 in a light-tight fashion. The rear cover 72 further has a filmsupporting surface 72 a for backing the filmstrip 65 placed behind theexposure aperture 74 a.

Atop the cartridge chamber 75 are mounted the film winding wheel 16 anda light-shielding lid closing mechanism 77. The film winding wheel 16and the light-shielding lid closing mechanism 77 are engaged with aspool 66 b and a light-shielding lid 66 a of the cartridge shell 66through a top wall of the cartridge chamber 76. The light-shielding lidclosing mechanism 77 closes the light-shielding lid 66 a when thecartridge shell 66 is removed from the film unit 10 after the wholelength of the filmstrip 65 is wound up into the cartridge shell 66.

The exposure unit 69 is constituted of a shutter charge mechanism, ashutter release mechanism, a film winding-stopping mechanism, a framecounting mechanism, the taking lens 13 and viewfinder optical system 111a and 111 b (see FIG. 12) and other elements necessary for exposure,which are mounted to a base block portion 85. The exposure unit 69 isattached to the front of the exposure chamber 74.

The flash device 70 is constituted of a circuit board 87 having contactchips 87 a, 87 b and 87 c printed thereon, the flash projector 17, amain capacitor 41, a synchronizing switch 46, a pair of contact strips92 a and 92 b for a battery 21, a metal contact blade 93 and otherelements constituting a flash circuit. The metal contact blade 93 isplaced in front of the film roll chamber 76 such that the metal contactblade 93 is brought into contact with the contact chips 87 a to 87 cwhen the charging operation member 56 is set to the ON position. Therebythe flash circuit starts charging the main capacitor 41. The flashprojector 17, which is mainly constituted of a flash discharge tube 42(see FIG. 11), a holder 89 for holding the flash discharge tube 42, anda diffusion plate 90 for diffusing light from the flash discharge tube42, is mounted to the circuit board 87. The synchronizing switch 46 isturned on in cooperation with releasing operation of the shutter releasemechanism of the exposure unit 69.

As shown in FIG. 10, the front cover 71 consists of a front cover mainbody 95 and a front panel 96 that is attached to the front of the frontcover main body 95. The front cover main body 95 has an opening 14 bthat is substantially equal in shape and size to an opening 14 a formedthrough the front panel 96, and is disposed in alignment with theopening 14 a. The openings 14 a and 14 b constitute the finder objectivewindow 14. The charging operation member 56 and a view changing plate 82are mounted in between the front panel 96 and the front cover main body95.

The view changing plate 82 has a round center hole 102 which is fittedon the lens barrel 99 so the view changing plate 82 is rotatable aboutan optical axis of the taking lens 13. The view changing plate 82 isurged by the toggle spring 105 to rotate either in a clockwise directionor in a counterclockwise direction. A coiled end 105 a of the togglespring 105 is fitted on a pin 103 that is formed on the front cover mainbody 95, and another end 100 b of the toggle spring 105 is inserted in asmall hole 104 of the view changing plate 82. A boss 106 is integrallyformed on a lower front portion of the view changing plate 82. The boss106 is inserted in the arced slot 58 that is formed under a lens hood 97of the front panel 96. The view field switching knob 57 is attached fromthe front to the boss 106.

The view changing plate 82 has in its peripheral portions a panoramicsize view window 112 (aspect ratio 3.0) and a conventional size viewwindow 113 (aspect ratio 1.5), and a cutout 114 disposed between thesewindows 112 and 113. By operating the view changing knob 57 to rotatethe view changing plate 82, one of the panoramic size view window 112,the conventional size view window 113 and the cutout 114 is placed inthe finder objective window 14. In this film unit 10, every pictureframe is recorded in the high-vision size, so that the finder objectivewindow 14 and the finder eyepiece window 14 c originally provide ahigh-vision size view field, and the high-vision size view field isprovided when the cutout 114 is placed in the finder objective window14. When the conventional size view window 113 is inserted in the finderobjective window 14, the field of view is limited to the conventionalsize. When the panoramic view window 112 is inserted in the finderobjective window 14, the field of view is limited to the panoramic size.

A cam slot 116 is formed in a peripheral range around the round hole102. The cam slot 116 accepts a pin 117 a which is formed on a tip of anarm 117 of a rotary lever 83 that is mounted above the exposure chamber74. Thus, the rotary lever 83 rotates along with the movement of theview changing knob 57. Although it is not shown in detail in thedrawings, there are provided below the exposure chamber 74 behind alight-shielding plate 81, a couple of data recording holes forphotographically recording print format data on the filmstrip 65, a dataswitching plate for opening or closing one or both of the data recordingholes, and a light guide for transmitting light from a data recordinglight emission element 136 (see FIG. 11) to the data recording holes.The data recording light emission element 136 is mounted to the flashdevice 10, and emits light upon each shutter release operation. Anotherarm 118 of the rotary lever 83 is coupled to the data switching plate,so that the data switching plate moves as the rotary lever 83 rotateswith the rotation of the view changing plate 82. As a result, both orone of the two data recording holes is closed or opened, so that at mosttwo dots are recorded as the print format data onto the filmstrip 65outside the frame exposure area in accordance with the view field. Inaccordance with the print format data, a print of the same size as theview field, e.g. a panoramic size print, is made from the high-visionsize picture frame.

FIG. 11 shows the flash circuit formed on the circuit board 87. Theflash circuit is of the auto charging type like the embodiment shown inFIG. 5, and is mainly constituted of a recording lamp section 133including the data recording light emission element 136, a boostersection 20 and a charging-discharging section 40. The data recordinglight emission element 136 emits light each time the synchronizingswitch 46 is turned on independently of the flash discharge tube 42.

The booster section 20 is constituted of the battery 21, an oscillationtransistor 22, an oscillation transformer 23, a rectifying diode 25, astopping transistor 38, and an indication light emission element 141 infundamentally the same way as above embodiments. Thecharging-discharging section 40 also has fundamentally the sameconstruction as the above embodiments, and is constituted of the maincapacitor 41, the flash discharge tube 42, a triggering electrode 42 a,a triggering capacitor 44, a triggering transformer 45, thesynchronizing switch 46, a flash charge switch 51, a flash selectionswitch 54 and so forth. The main capacitor 41 is connected in parallelto the flash discharge tube 42, and is connected at its minus pole to acathode of the rectifying diode 25.

The oscillation transistor 22 and the oscillation transformer 23constitute a well-known blocking oscillator circuit which startsoscillating when the flash charge switch 51 is turned on. While theoscillation transistor 22 oscillates, an alternating current of a highvoltage is induced across a secondary coil 32 of the oscillationtransformer 23 in accordance with a turn ratio of the secondary coil 32to a primary coil 31. The current from the secondary coil 32 is suppliedto the charging-discharging section 40 through the rectifying diode 25.

The base of the stopping transistor 38 is connected to a Zener diode 37.The Zener diode 37 conducts a Zener current when the main capacitor 412is charged up to a given voltage. The Zener current turns on thestopping transistor 38, thereby turning off the oscillation transistor22. When the main capacitor 41 is charged up to the set voltage, theindication light emission element 141 begins to light.

The flash selection switch 54 opens or closes a discharging circuit thatconsists of the triggering capacitor 44, a primary coil 45 a of thetriggering transformer 45 and the synchronizing switch 46. The flashselection switch 54 is also connected to a charging circuit for chargingthe main and triggering capacitors 41 and 44. Accordingly, turning offthe flash selection switch 54 prevents the triggering capacitor 44 fromdischarging and also prevents the main and triggering capacitors 41 and44 from charging. The flash charge switch 51 and the flash selectionswitch 54 have a common minus terminal.

The above flash circuit restarts charging automatically after a flashlight is projected so long as the flash charge switch 51 and the flashselection switch 54 are ON. Even after the main capacitor 41 is fullycharged, if the flash charge switch 51 and the flash selection switch 54are ON, the blocking oscillator circuit automatically restartsoscillating each time the voltage across the main capacitor 41 goesbelow the set charge voltage. Therefore, the main capacitor 41 ischarged repeatedly, and the indication light emission element 141 emitslight continually.

The charging operation member 56 has a button portion 120 that isexposed to the front of the front cover 71, a base plate 121 that ismounted to the front of the front cover main body 95, and an engagingportion 124 that is inserted in a vertical slot 122 formed through thefront cover main body 95, and is engaged with a pin 123 formed on afront side of the charge condition indicator 60. The charging operationmember 56 is thus slidable along the slot 122.

The base plate 121 has a vertical slit 126, which accepts a pin 127 thatis formed on the front wall of the front cover main body 95. The slit126 has not-shown two notches, so that the pin 127 clicks with either ofthe notches when the charging operation member 56 is slid up to the ONposition or down to the OFF position. Thereby, the charging operationmember 56 is held in the ON position or the OFF position. A narrow slit128 is formed beside the slit 126 for giving a resiliency to the slit126.

The button member 120 is disposed in front of the opening 88, and has anot-shown boss in its rear side. When the button member 120 is slidupward, the boss pushes the metal contact blade 93 through the opening88. Then, contact tips 93 a, 93 b and 93 c of the metal contact blade 93are respectively brought into contact with the contact chips 87 a, 87 band 87 c formed on the circuit board 87 of the flash device 70. Sincethe contact chips 87 a to 87 c and the metal contact blade 93 constitutethe flash charge switch 51 and the flash selection switch 54, the flashdevice 70 keeps charging so long as the charging operation member 56 isset in the upper ON position.

As shown in FIGS. 12 to 15, the charge condition indicator 60 is formedfrom a transparent plastic material, and consists of a mounting portion161 with a mounting sleeve 160 and a light guide portion 162 forconducting light from the indication light emission element 141 byinternal reflection. As shown in FIG. 12, the charge condition indicator60 is attached to a lens holder portion 163 that is formed integrallywith the base block portion 85 of the exposure assembly 69 and holds theviewfinder optical system 111 a and 111 b. The lens holder portion 163has a guide pin 164 and a supporting rail 165 formed integrallytherewith. The mounting sleeve 160 is fitted on the guide pin 164,whereas the supporting rail 165 supports the back of the light guideportion 162. A flange 166 for holding the mounting portion 161 is formedat a lower end of the guide pin 164 integrally therewith.

The light guide portion 162 has a first reflection surface 168 thatfaces the indication light emission element 141 when the chargingoperation member 56 comes to the ON position, a second reflectionsurface 169 that directs the light from the first reflection surface 168upwards, a light projecting end 170 for projecting the light from thesecond reflection surface 169 outside the film unit 10 for showing thecompletion of charging. The light guide portion 162 further has areflection surface 171 for reflecting the light from the secondreflection surface 169 toward an optical axis of the viewfinder opticalsystem 111 a and 111 b.

The light projecting end 170 has a pair of oppositely inclinedreflection surfaces 170 a and 170 b for projecting the light forward andrearward of the film unit 10, so that both the photographer and theperson to photograph can see when the flash device 70 is charged up.Therefore, not only the photographer can confirm that the film unit 10gets ready for a flash photograph, but alos the person to photograph canpose after the photographer gets ready to take a flash photograph.Because of the third reflection surface 171, the photographer can seethe light from the indication light emission element 141 while lookinginto the finder eyepiece window 14 c, so that the photographer can seethe completion of charging without stopping framing.

The operation of the film unit 10 shown in FIG. 7 will be brieflydescribed.

First, the view changing knob 57 is operated to change over the field ofview between the high-vision size, the panoramic size and theconventional size by inserting one of the panoramic size view window112, the conventional size view window 113 and the cutout 114 of theview changing plate 82 into the viewfinder objective window 14, forassigning a corresponding print format to each picture frame. Incooperation with the view changing plate 82, the rotary lever 83 rotatesto slide the data switching plate behind the light-shielding plate 81.Thereby, dots of a number corresponding to the view field may berecorded as the print format data on the filmstrip 65.

When taking a flash photography, the charging operation member 56 isslid from the lower OFF position to the upper ON position. When thecharging operation member 56 is in the OFF position, the chargecondition indicator 60 is located inside the film unit 10 as shown inFIGS. 7 and 14. As the charging operation member 56 is slid to the ONposition, the engaging portion 124 of the charging operation member 56engaged with the pin 123 of the charge condition indicator 60 movesupward along the slot 122. Thereby, the charge condition indicator 60moves upward along the guide pin 164 and the supporting rail 165,protruding the light projecting end 170 out of the film unit 10 throughthe opening 61, as shown in FIGS. 8 and 15. At the same time, the firstreflection surface 168 comes to face the indication light emissionelement 141.

When the charging operation member 56 comes to the ON position, thenotch in the slit 126 of the base portion 121 of the charging operationmember 56 clicks with the pin 127 on the front cover main body 95, andthe boss formed on the back of the button portion 120 of the chargingoperation member 56 pushes the metal contact blade 93 of the flashdevice 70 through the opening 88 of the front cover main body 95. Thus,the contact tips 93 a to 93 c are brought into contact with the contactchips 87 a to 87 c of the circuit board 87, turning on the flash chargeswitch 51 and the charge selection switch 54. As a result, the blockingoscillator circuit consisting of the oscillation transistor 22 and theoscillation transformer 23 starts oscillating.

The high voltage current that flows through the secondary coil 32 duringthe oscillation is supplied to the charging-discharging section 40through the rectifying diode 25, and is charged in the main capacitor 41and the triggering capacitor 44. When the voltage across the maincapacitor 41 reaches the set charge voltage, the Zener current flowsthrough the Zener diode 37, so that the stopping transistor is turned onto stop charging.

When the main capacitor 41 is charged up to the set charge voltage, theindication light emission element 141 is turned on. The light from theindication light emission element 141 is conducted through the lightguide portion 162 to the light projecting end 170, and is projectedconcurrently forward and rearward of the film unit 10 by being reflectedfrom the reflection surfaces 170 a and 170 b. Thus, the photographer andthe person to photograph simultaneously see when the flash device 70 ischarged up. Since the light from the indication light emission element141 is conducted to the viewfinder optical system 111 a and 111 bthrough the second and third reflection surfaces 169 and 171, thephotographer can confirm the completion of charging while framing.

When the photographer press the shutter button 18, the shutter mechanismof the exposure unit 19 is released, and the synchronizing switch 46 isturned on in cooperation with the shutter releasing. As a result, theflash discharge tube 42 discharges through the flash selection switch54, and thus a flash light is projected from the flash projector 17toward the subject. The light reflected from the subject is focused ontothe filmstrip 65 through the taking lens, recording a picture frame.When the synchronizing switch 46 is turned on, the data recording lightemission element 136 is also turned on for a constant time tophotographically record the print format data on the filmstrip 65 on amargin of the picture frame.

To take a photograph without flash light, the shutter button 18 ispressed while the charging operation member 56 is set to the OFFposition. Upon the synchronizing switch 46 being turned on incooperation with the shutter releasing, the flash device 70 does notflash at that time, but the data recording light emission element 136 isturned on for the constant time. Thereby, the print format data isphotographically recorded on the filmstrip 65 in correspondence with thesize of the view field selected at that time.

By setting the charging operation member 56 to the ON position after anexposure, the flash device 70 automatically starts charging for the nextexposure. So long as the charging operation member 56 is in the ONposition and thus the flash charge switch 51 and the flash selectionswitch 54 are in the ON condition, the blocking oscillator circuitoperates continually and the indication light emission element 141 emitslight continually even after the completion of charging the maincapacitor 41. Accordingly, it is easy to know whether the chargingoperation member 56 is in the ON position or not, so that the chargingoperation member 56 will be reset to the OFF position without fail whenthere is no need for charging. In this way, the film unit 10 of FIG. 7solves the problem of wasting the battery 21 so much that the battery 21is run down and the flash device 70 does not work any further.

Although the reflection surfaces 170 a and 170 b of the light projectionend 170 of the charge condition indicator 60 are provided in a recessformed in the upper end of the light guide portion 162 in the aboveembodiment, it is possible to provide the reflection surfaces 170 a and170 b directly at the upper end of the light guide portion 162, as shownin FIG. 16.

It is also possible to provide a charge condition indicator 60 with alight projecting portion 180 that is tapered to an upper tip, as shownin FIG. 17, or a light projecting portion 182 that is tapered to anupper tip and has grooves 181 around its periphery, as shown in FIG. 18,or a light projecting portion 184 that is tapered to an upper tip andhas a recess 183 in the upper tip, as shown in FIG. 19.

Furthermore, it is possible to provide a charge condition indicator 60with a light projecting portion 189 that consists of a centercylindrical portion 186 and radial cutouts 187 and radial ribs 188formed around the cylindrical portion 186, as shown in FIG. 20. Theshape of the light projecting portion of the charge condition indicator60 should not be limited to those shown in the drawings, but variousmodifications are possible so far as it can project light such that thephotographer and the person to photograph simultaneously see the lightfrom the indication light emission element 141.

In the above embodiments, the charge condition indicator 60 is formedfrom a transparent plastic material, such as polystyrene. But it ispossible to form the charge condition indicator 60 from asemi-transparent or colored transparent plastic material or glass. It isalso possible to form the charge condition indicator 60 from anon-colored transparent or semi-transparent material, and design theindication light emission element 141 to project colored light. Also, asemi-transparent plastic material mixed with a light diffusing agent maybe used to form the charge condition indicator 60. It is possible toform the charge condition indicator 60 integrally with the chargingoperation member 56.

In the above embodiment, the device for indicating the completion ofcharging the flash device 70 is constituted of the indication lightemission element 141 secured to the circuit board 87 of the flash device70, and the charge condition indicator 60 that has the light guideportion 162 for conducting light from the indication light emissionelement 141 and is slidable to protrude out of the film unit 10. It isalternatively possible to constitute a device for indicating completionof charging by an indication light emission element 141 and a holder 190holding the indication light emission element 141 therein, as shown inFIG. 21. The holder 190 is formed from a transparent plastic materialand is coupled to a charging operation member 56 such that an uppercover portion 190 a of the holder 190 protrudes out of a film unit 10,as shown in FIG. 22, by sliding the charging operation member 56 upwardto an ON position. The same elements are designated by the samereference numbers as in the above embodiments, so the description ofthese elements are omitted.

A terminal 141 a of the indication light emission element 141 is inresilient contact with a flash circuit board 87, and is brought intocontact with a conductive surface 192 formed on the flash circuit board87 when the holder 190 moves upward along with the charging operationmember 56. Since a current flows through the conductive surface 192 atthe completion of charging, the indication light emission element 141emits light at that time. The light from the indication light emissionelement 141 is radiated through the upper cover portion 190 a of theholder 190, so that the person to photograph as well as the photographernotices that the charging is complete.

According to the embodiment shown in FIG. 21, the light indicating thecompletion of charging may have a larger intensity than when the lightis projected through the light guide. Therefore, the charging conditioncan be seen from a distant. The terminal 141 a of the indication lightemission element 141 and the conductive surface 192 may also be used asa power switch for the flash circuit.

Instead of providing the indication light emission element 141 with theterminal 141 a that is brought into contact with the conductive surface192 of the flash circuit board 87 as the holder 190 is moved upward, itis possible to connect the indication light emission element 141 to theflash circuit on the circuit board 87 through a flexible wiring cord.The wiring cord should have a length that permits the indication lightemission element 141 to move together with the holder 190.

Any of the above described devices for indicating completion of chargingare simple in construction, and are able to produce at a low cost.

FIG. 23 shows an improvement over the flash circuit of FIG. 5. In theflash circuit of FIG. 23, a switch section, which doubles as a flashcharge switch and a flash selection switch, is constituted of aresilient conductive metal blade 195 and first to third contact chips196 a, 196 b and 196 c. The contact chips 196 a to 196 c are formed on aflash circuit board. The conductive metal blade 195 has a free end thatforks off in two tips 195 a and 195 b, and a fixed end 196 c that issoldered on the third contact chip 196 c. Without any load, the free end195 a and 195 b is set away from the flash circuit board. When thecharge operation member 50 is slid to the ON position, the chargeoperation member 50 presses the conductive metal blade 195, bringing thefree end tips 195 a and 195 b into contact with the first and secondcontact chips 196 a and 196 b. Thus the swtich section, i.e. the flashcharge switch and the flash selection switch, is held in the ONposition.

In the above embodiment, the forked free end 195 a and 195 b of themetal blade 195 ensures the tight contact with the first and secondcontact chips 196 a and 196 b and thus ensures the electric connectionbetween the contact chips 196 a to 196 c. However, the free end of themetal blade 195 does not have to be forked if only the metal blade 195is able to electrically connect the first to third contact chips 196 ato 196 c to each other. The metal blade 195 may be secured to any one ofthe first to third contact chips 196 a to 196 c. It is also possible toseparate the metal blade 195 from any contact chips 196 a to 196 c inthe OFF position, and bring the metal blade 195 into contact with thecontact chips 196 a to 196 c in the ON position, though securing one endof the metal blade to one contact chip like the present embodiment iseffective to lower the probability of contact failure.

The flash circuit of FIG. 23 is applicable to the film unit shown inFIG. 7. In that case, a data recording circuit like the recording lampsection 133 shown in FIG. 11 should be added to the flash circuit ofFIG. 23. Alternatively, it is possible to combine the flash circuit ofFIG. 23 with the charging operation member 56 and the charge conditionindicator 60 shown in FIG. 10 to provide a flash device for a film unithaving no data recording function. In this alternative, when thecharging operation member 56 is slid to the ON position, the metalcontact 195 connects the contact chips 196 a to 196 c to each other.Simultaneously, the charge condition indicator 60 slides together withthe charging operation member 56 to protrude outside the film unit 10,so that the light from the light emission element 52 is projectedthrough the charge condition indicator 60.

INDUSTRIAL APPLICATION FIELD

As described so far, the present invention is applicable to a flashdevice for a film unit preloaded with film, and also to a flash devicefor a compact camera capable of exchanging film and a separate flashdevice attached to and removable from a camera body as well.

What is claimed is:
 1. A flash device comprising an oscillation circuit that starts oscillating when a flash charge switch is turned on, the oscillation circuit comprising an oscillation transformer having a primary coil connected to a power source and a secondary coil connected to a main capacitor, the secondary coil being inductively coupled to the primary coil such that a high voltage current is induced in the secondary coil while the oscillation circuit oscillates, and that the main capacitor is charged with the high voltage current up to a set charge voltage, the flash circuit being characterized by comprising: a tap point located at an intermediate position of the secondary coil, the tap point having a potential that changes proportionally to the charge voltage across the main capacitor; a Zener diode connected to the tap point, to conduct a Zener current when the potential at the tap point reaches a value that corresponds to the set charge voltage of the main capacitor; and a stopping transistor activated by the Zener current to stop the oscillation circuit from oscillating and thus stop charging the main capacitor when the main capacitor reaches the set charge voltage.
 2. A flash device as claimed in claim 1, characterized in that the oscillation circuit includes an oscillation transistor which is deactivated by the stopping transistor to stop the oscillation circuit from oscillating.
 3. A flash device as claimed in claim 2, characterized in that the primary coil is connected at one terminal to a plus pole of the power source and at the other terminal to a minus pole of the power source through a collector-emitter circuit of the oscillation transistor, and the secondary coil is connected at one terminal to the main capacitor and at the other terminal to a base of the oscillation transistor; that the oscillation transformer further has a tertiary coil inductively coupled to the primary and secondary coils, the tertiary coil being connected in parallel to the primary coil relative to the power source, and connected at one terminal to the plus pole of the power source through the flash charge switch and at the other terminal to the base of the oscillation transistor; and that an base of the stopping transistor is connected to a cathode of the Zener diode, and an emitter and an collector of the stopping transistor are connected to the base and the emitter of the oscillation transistor respectively, wherein a potential difference between the tap point and the base of the oscillation transistor is applied across the Zener diode and causes the Zener diode to conduct the Zener current when the main capacitor reaches the set charge voltage, and the oscillation circuit is deactivated as the base of the oscillation transistor is connected to the emitter thereof through the stopping transistor when the stopping transistor is turned on by the Zener current.
 4. A flash device as claimed in claim 1, characterized by comprising a rectifying diode connected between the tap point and the Zener diode, the rectifying diode conducting current only in the same direction as the Zener current.
 5. A flash device as claimed in claim 4, wherein a temperature coefficient of a forward voltage of the rectifying diode has an opposite polarity to a temperature coefficient of a Zener voltage of the Zener diode, such that the Zener diode and the rectifying diode form a mutual temperature compensating circuit.
 6. A flash device comprising an oscillation circuit having an oscillation transformer, the oscillation transformer having a primary coil connected to a power source and a secondary coil connected to a main capacitor, the secondary coil being inductively coupled to the primary coil such that a high voltage current is induced in the secondary coil while the oscillation circuit oscillates, and that the main capacitor is charged with the high voltage current, the flash circuit being characterized by comprising: a tap point located at an intermediate position of the secondary coil, the tap point having a potential that changes proportionally to the charge voltage across the main capacitor; a Zener diode connected to the tap point, to conduct a Zener current when the potential at the tap point reaches a value that corresponds to a set charge voltage of the main capacitor; a stopping capacitor charged with the Zener current; and a stopping transistor connected to the stopping capacitor through a resistor, the stopping transistor being turned on to deactivate the oscillation circuit while a current discharged from the stopping capacitor is applied through the resistor, thereby the stopping transistor being turned on for a time enough to deactivate the oscillation circuit and stop charging the main capacitor.
 7. A flash device as claimed in claim 6, characterized in that the oscillation circuit can be switched over between an active state for charging the main capacitor and an inactive state for not charging the main capacitor, wherein so long as the oscillation circuit is maintained in the active state, the flash circuit restarts charging the main capacitor after the stopping capacitor is discharged, and keeps charging the main capacitor intermittently after the main capacitor is charged up to the set voltage.
 8. A flash device as claimed in claim 7, characterized in that the oscillation circuit includes an oscillation transistor which is deactivated by the stopping transistor to stop the oscillation circuit from oscillating.
 9. A flash device as claimed in claim 8, characterized in that the primary coil is connected at one terminal to a plus pole of the power source and at the other terminal to a minus pole of the power source through a collector-emitter circuit of the oscillation transistor, and the secondary coil is connected at one terminal to the main capacitor and at the other terminal to a base of the oscillation transistor; that the oscillation transformer further has a tertiary coil inductively coupled to the primary and secondary coils, the tertiary coil being connected in parallel to the primary coil relative to the power source, and connected at one terminal to the plus pole of the power source through a flash charge switch and at the other terminal to the base of the oscillation transistor; that an base of the stopping transistor is connected to a cathode of the Zener diode through the resistor, and an emitter and an collector of the stopping transistor are connected to the base and the emitter of the oscillation transistor respectively; and that the stopping capacitor is connected at one terminal to the base of the oscillation transistor and at the other terminal to the cathode of the Zener diode and thus the base of the stopping transistor through the resistor, wherein a potential difference between the tap point and the base of the oscillation transistor is applied across the Zener diode and causes the Zener diode to conduct the Zener current when the main capacitor reaches the set charge voltage, and the oscillation circuit is deactivated as the base of the oscillation transistor is connected to the emitter thereof through the stopping transistor while the stopping transistor is turned on by the current discharged from the stopping capacitor through the resistor.
 10. A flash device as claimed in claim 6, characterized by comprising a rectifying diode connected between the tap point and the Zener diode, the rectifying diode conducting current only in the same direction as the Zener current.
 11. A flash device as claimed in claim 10, wherein a temperature coefficient of a forward voltage of the rectifying diode has an opposite polarity to a temperature coefficient of a Zener voltage of the Zener diode, such that the Zener diode and the rectifying diode form a mutual temperature compensating circuit. 